How to keep LED stay ON while waiting input from serial communication

Hi, I am writing a code to detect the input from serial communication. If the arduino detected "abc123" , LED will ON, else LED OFF. My problem is the LED on just for a while when receiving "abc123". After that, it turns off while waiting for the next serial input. Below is my code:

char data;
void setup() {
Serial.begin(9600);
}

void loop() {
if(Serial.available() > 0)
{
data = Serial.read();
}

if (data == "abc123"){
digitalWrite(13,HIGH);
}
else{
digitalWrite(13,LOW);
}
}

How can I keep the LED on while waiting for the next serial input? Thank you.

Before you start, learn how to turn ON a LED.

Next learn about character arrays.

Then search for serial input basics tutorial.

You can't compare a single character with a string of text.

I have changed to String data in my code, but the problem still the same.

And what happens with the LED?

See post #2

Also, when you revise code, post the new version so we can see which changes you made.

Check out my tutorial Arduino Software Solutions which as various ways to read from Serial using Strings and SafeStrings.

Lets assume you are terminating the input with a \n. This sketch will read a line (see the tutorial for other example sketches)

// readStringUntil_nonBlocking.ino
// Reads chars into a String until newline '\n'
// https://www.forward.com.au/pfod/ArduinoProgramming/SoftwareSolutions/index.html
// Pros: Simple. Non-Blocking
// Cons: Does not return until the until_c char is found. i.e. no timeout or length limit

String input;

void setup() {
  Serial.begin(9600);
  for (int i = 10; i > 0; i--) {
    Serial.print(' '); Serial.print(i);
    delay(500);
  }
  Serial.println();
  Serial.println(F("readStringUntil_nonBlocking.ino"));
  input.reserve(80); // expected line size, see Taming Arduino Strings
  // https://www.forward.com.au/pfod/ArduinoProgramming/ArduinoStrings/index.html
}

// read Serial until until_c char found, returns true when found else false
// non-blocking, until_c is returned as last char in String, updates input String with chars read
bool readStringUntil(String& input, char until_c) {
  while (Serial.available()) {
    char c = Serial.read();
    input += c;
    if (c == until_c) {
      return true;
    }
  }
  return false;
}

void loop() {
  if (readStringUntil(input, '\n')) { // read until find newline
    Serial.print(F(" got a line of input '")); Serial.print(input); Serial.println("'");
    input = ""; // clear after processing for next line
  }
}

Then you can edit the loop to add your check and turn the Led ON

  if (readStringUntil(input, '\n')) { // read until find newline
    Serial.print(F(" got a line of input '")); Serial.print(input); Serial.println("'");
    input.trim();
    if (input == "abc123") {
      digitalWrite(13,HIGH);
    } else{
     digitalWrite(13,LOW);
    }
    input = ""; // clear after processing for next line
  }

That will keep the line ON until the next line is read in.
You do not say when the LED should turn Off.

Nice bit of work !

Did you change it to:
data = Serial.readString();
Is the line ending in Serial Monitor set to "No line ending"?